Abstract
Inflammation is pivotal to fight infection, clear debris, and orchestrate repair of injured tissues. Although Drosophila melanogaster have proven invaluable for studying extravascular recruitment of innate immune cells (hemocytes) to wounds, they have been somewhat neglected as viable models to investigate a key rate-limiting component of inflammation-that of immune cell extravasation across vessel walls-due to their open circulation. We have now identified a period during pupal development when wing hearts pulse hemolymph, including circulating hemocytes, through developing wing veins. Wounding near these vessels triggers local immune cell extravasation, enabling live imaging and correlative light-electron microscopy of these events in vivo. We show that RNAi knockdown of immune cell integrin blocks diapedesis, just as in vertebrates, and we uncover a novel role for Rho-like signaling through the GPCR Tre1, a gene previously implicated in the trans-epithelial migration of germ cells. We believe this new Drosophila model complements current murine models and provides new mechanistic insight into immune cell extravasation.
Highlights
Following damage to, or infection of, vertebrate tissues, circulating leukocytes must be recruited to the wound site from the circulation
Leukocyte transmigration through the vessel wall (“diapedesis”) involves a coordinated series of complex molecular and morphological changes in both immune cells and endothelial cells lining that local region of the venule (Voisin and Nourshargh, 2013; Muller, 2015, 2016; Vestweber, 2015)
To determine whether there might be a suitable stage during Drosophila pupal development to model immune cell diapedesis, we examined the distribution of hemocytes throughout wing morphogenesis
Summary
Infection of, vertebrate tissues, circulating leukocytes must be recruited to the wound site from the circulation. Drosophila immune cells extravasate from wing veins to sites of tissue damage Using the distal-most region of 75-h APF pupal wings, we generated small 40-μm-diameter laser wounds within the wing epithelium at ∼40 μm from vein L3 (Fig. 2, A and B).
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